She said: "I wanted a Jewish name because my fiance is a Jew and the name is the male version of Esther. We found it in a name book and liked it."

The socialite, who is due to give birth in two months, added: "I love being pregnant, my fiance has to cook for me, I'm so exhausted all the time but I love it."

She said her father, charity campaigner Bob Geldof, cannot wait for the birth.

"He's happy there is going to be a boy in the family, there will finally be an heir to the throne of Geldof. My father is so ecstatic, if this was medieval England I would be in the money."

She added: "I think having a baby will be a positive change in my life, we have a house and dog now."

Speaking about the designer, Geldof said: "I've been wearing Temperley a lot because it fits me. I can't wear anything with zips and constraints at the moment. When I'm at home I'm just in Primark pyjamas though, not very glamorous."

In September Pippa Middleton prompted a flurry of flashbulbs when she graced the front row of the Temperley show.

Geldof said the Duchess of Cambridge and her sister had changed British fashion. She said: "They have proved you can be conservative and sexy, it's Sloaney couture and I like that. I like the Sloane ranger look."